Fig. 1.

Examples of immunoglobulin G (IgG) and non-IgG-based binding reagents developed for use as research tools. One of the major advantages provided by the many IgG alternatives is their smaller size, as demonstrated by the IgG scale bars with all alternative reagents compared to scale. IgG-based reagents include the fragmented versions, fragment of antigen binding (Fab) and single-chain fragment of variability (ScFv) as well as the reformatted Camelid IgG (Nanobody). Non-IgG-based reagents [Designed Ankyrin Repeat Proteins (DARPins), Monobodies, Anticalins, Affibodies] demonstrate even smaller sizes, with Affibodies approaching 1 nm in diameter compared to the 10-nm diameter measured by the IgG antigen-binding region. PyMOL (Schrödinger, LLC, New York, NY) and KeyNote (Apple Inc., Cupertin, CA) were used to create the images